Fluid pumps are well known, have been utilized in both commercial and residential applications and involve a wide variety of design types, e.g., positive displacement, venturi and the like. One design type, a cylindrically-shaped centrifugal pump sometimes referred to as a "flinger" pump, is widely used to pump water out of water wells. Examples of such fluid pumps are described in U.S. Pat. Nos. 4,708,589 (Nielsen et al.) and 4,923,367 (Zimmer).
Such pumps are preferred for water wells, e.g., residential wells, since they can be configured to have a relatively small diameter to readily fit into a well hole. Notwithstanding, multistage centrifugal pumps have substantial pumping capacity.
Each "stage" of such a pump has an impeller which "flings" water radially outward by centrifugal force. All impellers are driven by a common central shaft attached to a sealed electric motor. Each stage also includes a diffuser and a suction cap and such stages (perhaps seven in number) are "stacked" end-to-end so that the discharge portion of one stage feeds liquid into the inlet portion of the next stage.
When so stacked (and assuming the pump housing is not in place), the circular edges of the diffuser and the suction cap are visible. The impeller is confined within the stack and is not visible.
At one end of the stack is an adapter for receiving and mounting the electric motor. At the other end of the stack is an output flange from which water flows and to which is attached a pipe leading to the building for which water is being supplied.
For reasons relating to leakage prevention and pump efficiency, it is desirable to retain the pump stages and the adapter and output flange snugly compressed against one another. In one exemplary type of prior art pump as shown in the aforementioned Nielsen et al. patent, stage/adapter/flange compression is by a hollow, cylindrical metal housing sleeved over the stacked stages.
One way compression is maintained is by crimping the housing to the adapter and output flange. Another way is to form threads on the exteriors of the adapter and the output flange and on the interior of the housing at the housing ends. The adapter and the flange are then screwed to respective ends of the housing. The adapter and flange may be prevented from rotating by a set screw or other fastener.
In another type of pump as shown in the aforementioned Zimmer patent, the housing is embodied as a pair of plastic half-cylinders joined together by fasteners. Compression of the stages is provided by an adjustment cone rather than by the housing.
In yet another type of prior art pump, believed to be made by Morris Industries, it is understood that a composite housing made by winding filaments is substituted for the metal sleeve-like housing. That is, such composite housing (which is understood to be threaded at both ends or at least have threaded fasteners at such ends) is sleeved over the stacked stages and then screwed to the adapter and output flange.
While these prior art pumps have been generally satisfactory for their intended purpose, they tend to be characterized by certain disadvantages. For example, the compressive force holding the stages against each other can decrease over time. As a result, the stages (or parts of stages) may separate slightly and leaks develop. And in a more extreme case, the diffuser and/or the suction cap (both of which are subjected to torsional forces by the moving water in the pump) may rotate. This is so since in known pumps, the sole force preventing rotation is compression force and if such force diminishes sufficiently, rotation results. In other words, sleeved housings do not per se exert countertorque on the diffuser or suction cap. Either leakage or unwanted rotation of pump parts results in a decrease in pump performance.
And another disadvantage arises merely from the fact that many known pump housings are metal, i.e., stainless steel. Such housings are relatively thin walled and may dent if dropped. In a severe case, a diffuser or suction cap within the housing may be fractured.
And if ordinary steel is selected as a housing material or for other components, rust and corrosion are sure to occur soon after the onset of pump use. For example, a metal set screw securing the adapter and output flange to the housing can corrode and become displaced resulting in formation of an opening in the housing through which water can escape resulting in decreased performance. Further, for a housing of given dimensions including wall thickness, metal housings weigh more than those made with alternative materials such as plastic. Plastic and composites, are also typically less expensive than materials such as stainless steel.